Method of controlling a wiper motor

ABSTRACT

A method and a device for controlling a wiper motor ( 30 ) of a motor vehicle are described. A rain sensor ( 32 ) sends signals (S) to a control device and the wiper motor ( 30 ) is switched off when a first threshold (S 1 ) is exceeded or is not reached. After a defined time period (T 1 ) after switching off the wiper motor ( 30 ), the wiper motor ( 30 ) is switched on in order to remove residual wetness when the signals (S) exceed or drop below a lower, second threshold (S 2 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device forcontrolling a wiper motor as recited in the preamble of the independentclaims. Numerous methods of controlling a wiper motor are known in whichthe response sensitivity of a rain sensor may be adjusted as a functionof an additional brightness sensor.

[0002] A method of adjusting the response sensitivity of a rain sensoris proposed in German Patent 41 34 432 in which the response sensitivitymay be adjusted by an additional brightness sensor or by a switch-onsignal of a light switch. In addition, it is known that theamplification of a rain sensor signal may be influenced by the externalprotective circuit as a function of the ambient brightness.

[0003] However, in all of these methods and devices, residual wetness isfrequently encountered on the windshield, which is particularlytroublesome, especially in darkness.

ADVANTAGES OF THE INVENTION

[0004] The method according to the present invention having thecharacterizing features of the main claim has the advantage thatresidual wetness, which may still be present on the windshield after thewiper motor has been switched off, is detected and removed.

[0005] After it has stopped raining, streaks often remain on thewindshield which do not dry by themselves and which may thus representresidual wetness. By re-evaluating the signals from the rain sensorafter a defined time after the wiping operation has ended and checkingagainst a second threshold, one or more additional wiping operations maybe triggered, as needed. In this way, the residual wetness is removed,thereby significantly improving visibility.

[0006] The measures recited in the subclaims result in advantageousrefinements to and improvements of the features characterized in themain claim.

[0007] An additional significant advantage is realized when this methodis supplemented by an ambient brightness signal, using a brightnesssensor, and the wiper motor is actuated at a defined change in theambient brightness. In this way, consideration is made for the fact thatresidual wetness on the windshield is even more troublesome in darknessthan in normal daylight.

[0008] This significant advantage is realized particularly when enteringtunnels or parking garages in which the ambient brightness quicklychanges from light to dark. If the wiper motor was in intermittentoperation, for example, before entering, the windshield is normally wetupon entering the tunnel. After entry has been recognized by detectionof the change in the ambient brightness, it possible to trigger a wiperoperation and thus remove troublesome residual wetness.

[0009] In such cases it is of further advantage when the wiper motor isactuated for only a single wiper cycle. Although residual wetness isgenerally troublesome, there is little associated moisture. The residualwetness may thus be removed in one wiper cycle, thereby preventingabrasive stress such as rattling or squeaking of the wiper on thewindshield.

[0010] Furthermore, it is particularly advantageous when the wiper motoris actuated only when a moisture exceeds or drops below a threshold ofthe rain sensor, since in this manner it is possible to prevent dryfriction of the wiper against the windshield.

[0011] The device according to the present invention has the advantagethat visibility-impairing residual wetness remaining on the windshieldcaused by unevaporated smears or drops may be removed.

[0012] It is particularly advantageous when the trigger stage has afirst threshold value analyzer which compares the signals to a firstthreshold and which is connected, via a delay element connected to atimer, to a second threshold value analyzer which compares the signalsto a second threshold and which triggers a single wiper cycle when thesecond threshold is exceeded or is not reached. A simple and practicaldevice for removing residual wetness on a windshield is thus provided.

[0013] If this device also has a brightness sensor, the trigger stageactuating the wiper motor at a defined change in brightness when thewiper motor has already been actuated within a predetermined time, thehistory of the wiping operation is thus advantageously taken intoaccount. If a continuous wiping operation was still in progress twominutes, for example, before a large change in brightness, it may beconcluded with reasonable certainty that residual wetness is stillpresent on the windshield.

[0014] In addition, it is particularly advantageous when the device hasa brightness analysis stage which compares the changes in signals fromthe brightness sensor to the defined change in brightness.

[0015] If the timer or the delay element also has a flag indicating awiper cycle which is reset only after a predetermined time has elapsed,it can be determined at any time whether a wiper cycle has beentriggered or ended within a predetermined historical time period.

[0016] It is of significant advantage if the evaluation stage isdesigned in such a way that it triggers a single wiper cycle only whenthe flag of the timer or delay element is simultaneously set and thethreshold of the defined change in brightness is exceeded or is notreached. Thus, a single wiper cycle is triggered only when thebrightness analysis stage gives a positive result and the last wipingoperation has taken place fairly recently, since in this case it can beconcluded that residual wetness is present on the windshield.

DRAWING

[0017] An exemplary embodiment of the present invention is illustratedin more detail in the drawing and in the following description.

[0018]FIG. 1 shows the method according to claim 1 in a schematicillustration.

[0019]FIG. 2 shows a device according to the present invention in aschematic illustration.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0020]FIG. 1 shows a schematic illustration of the method according tothe present invention. Signals S relayed in sensor step 10 represent ameasure of the moisture present on the windshield of a motor vehicle.Without limiting the generic character, it is assumed in the followingdescription that the greater the signal S, the greater the wetness onthe windshield, and therefore the greater the moisture.

[0021] In a first step 12 these signals are checked whether they exceeda specified first threshold S1, and thus, whether a given moisture levelhas been reached. First threshold S1 is a fixed threshold, but may alsobe variable. Numerous such methods are known, in particular methods inwhich threshold Si is controlled as a function of thee sensor signalitself, using a historical average value.

[0022] If the sensor signal drops below this first threshold S1, wipermotor 30 (FIG. 2) is switched off in a trigger stage 38, since themoisture on the windshield has decreased. At this point, however, thewindshield frequently still has residual wetness, from which it maygenerally be assumed that the residual wetness will most likely soondisappear by evaporating on its own. However, this is not always thecase. For this reason, in a second step 14 waiting is performed for adefined time Ti, and in a third step 16 it is checked for whether or notthe sensor signal is below a second threshold S2. This second thresholdS2 is lower than first threshold S1, and thus corresponds to a lowerdegree of moisture.

[0023] If the signal is below this second threshold S2, it is assumedthat the residual wetness on the windshield has disappeared due toevaporation or wind drifts, and that no further wiping operations willbe triggered. However, if this second threshold is exceeded or is notmet after time t has elapsed, it is assumed that residual wetness ispresent on the windshield, and a wiping operation is begun to remove theresidual wetness.

[0024] In one variation, after first threshold S1 has not been reached asignal for the ambient brightness may trigger a wiping operation. Tothis end, the changes in the signal for the ambient brightness aredetected in a brightness detection step 18 and a differential step 20,and when the value falls below a set, defined change, a wiping operationis triggered in a comparison step 22.

[0025] This addition is thus particularly practical, since residualwetness on the windshield is considered to be particularly troublesomewhen a tunnel or parking garage, for example, is entered. The suddenchange in ambient brightness H is detected, and then a wiping operationis triggered.

[0026] Of course, both options may be combined if desired, so that aspecific moisture threshold Sf must be present before a wiping cycle istriggered regardless of, for example, whether the defined change inambient brightness has been exceeded.

[0027]FIG. 2 shows a device according to the present invention forcontrolling wiper motor 30. A rain sensor 32, a timer 34, and abrightness sensor 36 send their signals to a trigger stage 38. Thistrigger stage 38 controls wiper motor 30.

[0028] Trigger stage 38 has a first threshold value analyzer 40 whichreceives signal S from rain sensor 32. The output of this firstthreshold value analyzer 40 is connected directly to wiper motor 30, andits other output is connected to a delay element 42.

[0029] Delay element 42 also has a flag F which is set when a wipercycle has ended. The flag is reset when defined time Ti has elapsed andflag F has not been reset in the meantime. Depending on the choice ofdefined time Ti, care must be taken that flag F is not set after a wipercycle which serves only to remove residual wetness.

[0030] Therefore, delay element 42 receives at its input the signal fromfirst threshold value analyzer 40 as well as the signal from timer 34.An output from delay element 42 is connected to a brightness analysisstage 44 which is also connected directly to wiper motor 30 and is ableto actuate the wiper motor.

[0031] Another output of delay element 42 is connected to secondthreshold value analyzer 46, which is also capable of triggering wipermotor 30.

[0032] Brightness analysis stage 44 includes a differential element 43,a brightness threshold stage 45, and a logic evaluator 47. The signalfrom brightness sensor 36 is sent to differentiating element 43, fromthere to brightness threshold stage 45, and then to logic evaluator 47,which activates wiper motor 30 depending on flag F.

[0033] The functioning of the device is explained in the followingdescription. Rain sensor 32 measures the wetness present on thewindshield. This signal S from rain sensor 32 is evaluated by firstthreshold value analyzer 12 to determine whether the signal has droppedbelow a first threshold S1, and thus whether the moisture has droppedbelow a given threshold, whereupon first threshold value analyzer 40switches off wiper motor 30. Signal S is then relayed to delay element42. The delay element is connected to timer 34. After the wiper motorhas been switched off by first threshold value analyzer 40, delayelement 42 sets flag F, which is designed as a simple high level on acontrol line. In addition, delay element 42 resets flag F after apredeterminable time T2. After a defined time T1 has elapsed, secondthreshold value analyzer 46 checks whether a second threshold S2, whichtypically is lower than first threshold S1, is still higher than secondthreshold S2.

[0034] If this is the case, an additional wiper operation is carried outby wiper motor 30 to remove this residual which is apparently present.As soon as flag F is set, brightness analysis stage 44 is activated. Thebrightness analysis stage receives the signal from brightness sensor 36,differentiates this signal, and activates wiper motor 30 only when adefined change in the ambient brightness is detected.

[0035] The algorithm for logic evaluator 47 may be freely chosen.

What is claimed is:
 1. A method of controlling a wiper motor (30), inparticular of a motor vehicle, a rain sensor (32) sending signals (S) toa control device and the wiper motor (30) being switched off when thesignal exceeds or drops below a first threshold (S1), wherein, followinga defined time period (T1) after the wiper motor (30) is switched off,the wiper motor (30) is switched on to remove residual wetness.
 2. Themethod as recited in claim 1, wherein the wiper motor (30) is switchedon after a defined time period (T1) only when the signals (S) exceed ordrop below a lower, second threshold (S2).
 3. The method as recited inclaim 1 or 2, wherein the ambient brightness is determined using abrightness sensor (36), and the wiper motor (30) is actuated at adefined change in the ambient brightness when the wiper motor (30) hasalready been actuated at least before a predeterminable time period(T2).
 4. The method as recited in claim 3, wherein the wiper motor (30)is actuated only when a moisture threshold (Sf) of a rain sensor (32) isexceeded or is not reached.
 5. The method as recited in one of thepreceding claims, wherein the wiper motor (30) is actuated for a singlewiper cycle.
 6. A device for controlling a wiper motor (30), inparticular for carrying out a method as recited in one of the precedingclaims, including a rain sensor (32) which sends signals (S) and a timer(34), wherein a trigger stage (38) is provided which switches on thewiper motor (30), which had been switched off after the signals (S)exceeded or dropped below a first threshold (S1), after a defined timeperiod (T1), to remove residual wetness.
 7. The device as recited inclaim 6, wherein the trigger stage is designed in such a way that itswitches on the wiper motor (30) after the defined time (T1) only whenthe signals (S) exceed or drop below a lower, second threshold (S2). 8.The device as recited in claim 7, wherein the trigger stage has a firstthreshold value analyzer (40) which compares the signals (S) to a firstthreshold (S1), the threshold value analyzer being connected, via adelay element (42) connected to a timer, (34) to a second thresholdvalue analyzer (46) which compares the signals (S) to a second threshold(S2) and triggers a single wiper cycle when the signals exceed or dropbelow the second threshold (S2).
 9. The device as recited in claims 6,7, or 8, wherein a brightness sensor (34) is provided, and the triggerstage (38) actuates the wiper motor, in particular for only one wipercycle, at a defined change in brightness when the wiper motor (30) hasalready been actuated at least before a predetermined time period (T2).10. The device as recited in claim 9, wherein the trigger stage (38) hasa brightness analysis stage (44) which compares the changes in signalsfrom the brightness sensor (36) to the defined change in brightness. 11.The device as recited in one of claims 7 through 10, wherein the timer(34) or the delay element (42) has a flag (F) indicating a wiper cyclewhich is reset only after a predetermined time period (T2) has elapsed.12. The device as recited in claim 11, wherein the trigger stage (38) isdesigned in such a way that it triggers a single wiper cycle forremoving residual wetness when the defined change in brightness isexceeded or is not reached and the flag (F) is set.